Photosensitive compositions are currently used in microlithography to form integrated circuits. These photosensitive compositions typically comprise a photoactive compound, a resin and a solvent. A coating of the photosensitive composition is formed on a substrate, the coating is imagewise exposed and developed to form an image in the coating. As the requirement for faster integrated circuits grows, so does the need to reduce the dimensions of the features printed on these circuits. One method of producing small features is to imagewise irradiate the photoresist with light of shorter wavelengths. The traditional photosensitive compositions which contained novolaks as resins and diazonaphthoquinones as photosensitive compounds worked well at wavelengths between 350 nm and 450 nm. However, with light of wavelengths less than 350 nm, and especially less than 250 nm, neither do the typical novolacs have sufficient transparency, nor do the diazonaphthoquinones have the necessary absorption characteristics to allow for photoresist images of adequate resolution and edge acuity to be formed. Therefore, it has become necessary to synthesize new resins and new photoactive compounds for use at shorter wavelengths.
Diazonaphthoquinone photoactive compounds used for irradiation wavelengths between 350 nm and 450 nm are known and described in the following patents, U.S. Pat. No. 4,588,670, U.S. Pat. No. 4,853,315, U.S. Pat. No. 5,501,936, U.S. Pat. No. 5,532,107 and U.S. Pat. No. 5,541,033, which are incorporated herein by reference.
Radiation-sensitive mixtures containing photoactive diazo derivatives which are suitable for irradiation with high-energy deep UV radiation have been described in the literature for some time.
U.S. Pat. No. 4,339,522 discloses positive-working radiation-sensitive mixtures which contain, as a photoactive compound, a diazo derivative of Meldrum's acid. This compound is said to be suitable for exposure to high-energy UV radiation in the range between 200 nm and 300 nm. However, this photoactive compound is lost under the elevated processing temperatures frequently employed in practice; the radiation-sensitive mixture loses its original activity, so that reproducible photoresist images are not obtained.
Further, positive-working photoactive compounds which are sensitive in the deep UV region are disclosed in U.S. Pat. No. 4,735,885. The compounds have the disadvantage that the carbenes formed from these on exposure do not have adequate stability in the matrix for the desired formulation of carboxylic acid. This results in an inadequate solubility difference between the exposed and the unexposed areas in the developer and thus leads to an undesirably high removal rate of the unexposed areas, leading to poor resolution.
U.S. Pat. No. 4,622,283 provide 2-diazocyclohexane- 1,3-dione or -cyclopentane-1,3-dione derivatives as photoactive compounds for radiation-sensitive mixtures of the type described. These compounds have lower volatility, but they exhibit, depending on the substitution pattern present, poor compatibility in the radiation-sensitive mixture. This can cause recrystallization in the solution or in the coating.
EP-A 0 195 986 proposes phosphoryl-substituted diazocarbonyl compounds as photoactive compounds, since these have a higher carbene stability. In practice, however, such compounds will probably not be widely accepted since phosphorus atoms are potentially used as dopants for the semiconductor substrates.
Photoactive compounds based on 3,diazo 4,oxo coumarin structure and sensitive in the shorter wavelengths are disclosed in JP 2,061,640. Additionally, JP 3,079,670, describes a photoresist based on a similar coumarin structure, and further includes 2-diazo 1-indanone and 3-diazo 2,4-quinolinedione as photosensitive compounds, wherein the photoresist when processed gives a negative image. These are monomeric diazo compounds that have substituents of low molecular weight, such as methyl, chlorine, methoxy, propyl, that can be susceptible to volatility, diffusion through the photoresist film, amongst other factors. Furthermore, the 3-diazo 2,4-quinolinedione described in JP 3,079,670 discloses as substituents only sulfonic acid, sulfonylhalogeno, alkoxy, hydrogen or halo groups and when processed in a photoresist composition gives negative images.
All of the references mentioned herein are incorporated by reference in their entirety.
The present invention describes a novel photoactive 3-diazo 2,4-quinolinedione compounds, where one of the benzyl substituents is a carbon containing organic ballast moeity that has a molecular weight greater than 75, and can provide solubility and stability to the novel photoactive compound in a photosensitive composition and its coating during lithographic processing. The invention further discloses a process for the preparation of the novel 3-diazo 2,4-quinolinedione compounds.